You'll probably only call this function if progress polling times out and its
error message tells you to call pollProgress
to resume.
pollProgress(progress_url, wait = 0.5, error_handler = NULL)
The percent completed of the progress. Assuming the
options(crunch.timeout)
(default: 15 minutes) hasn't been reached, this
will be 100. If the timeout is reached, it will be the last reported progress
value.